Ground and Neutral at panelboard

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Don

Don

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By running a EGC along with a GC tapped from the same point, [Xfmr or service] in the same raceway will create a code violation and provide parallel paths/loop between source and main/MDP/CBP etc.

The GC or neutral can only be used for grounding/bonding on the "line" side of a service or separately derived system. Thats the code. In the past we had a couple of exceptions with ranges and dryers etc.

Somebody figured it out back in the 99 cycle and the code was changed and inpectors in my area will not allow a EGC running side by side with a GC from a service or XFMR to a MDP/MD/CBP etc.

We used to run a EGC and GC together in such cases, but whats the point, for they are the same conductor and thus they "split" load and thats why the OP has his concerns about is meter registering current on a EGC.

P.S. we bond the XFMR case to the GC with a jumper inside the XFMR.
 
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Gmack said:
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By running a EGC along with a GC tapped from the same point, [Xfmr or service] in the same raceway will create a code violation and provide parallel paths/loop between source and main/MDP/CBP etc.
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Gmack I do not see the parallel path.

As far as I know we have been taking about a transformer installation.

We are only allowed by 250.30(A) (1) to bond at the transformer or at the first disconect but not both.

Because we only bond once there is no parallel path created by a EGC or bonding jumper as I would call it.

If we chose to use the exception 1 to 250.30(A)(1) and bond in both places than we are not allowed to establish a parallel path for the grounded circuit conductor by any means.

In my area I do not see people using the exception, they only bond once and that is generally at the transformer.
 
Iwire

Iwire

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Im talking about a separate "conductor/wire" istalled along side the "GC or neutral wire" from the XFMR to a MDP in the same raceway,. metallic or otherwise, tapped/common from XO.
 
Gmack said:
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Im talking about a separate "conductor/wire" installed along side the "GC or neutral wire" from the XFMR to a MDP in the same raceway,. metallic or otherwise, tapped/common from XO.
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I am not following you here, I am trying.

I bond at the transformer, from XO I run a grounded and a grounding conductor in the same raceway(s) to the first panel. At that panel the neutral bar is isolated from the enclosure, the grounding conductor is bonded to the panel enclosure. There is no parallel path unless some bonds the neutral downstream.
 
Iwire

Iwire

When "starting over" with a XFMR we are now talking "service".

First panel/MDP etc cannot be isolated. Main bonding.

Maybe I read you wrong.
 
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Gmack said:
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Im talking about a separate "conductor/wire" istalled along side the "GC or neutral wire" from the XFMR to a MDP in the same raceway,. metallic or otherwise, tapped/common from XO.
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Gmack, that's the problem, nobody else is directly talking about a separate conductor, the issue is bonding at two locations and outside metallic paths such as conduit and metallic studs.

You are right in your assessment that two conductors connected to XO in a transformer and connected to the same point in a Main would be a parallel conductor, and unless they meet the requirements of 310.4 they would be a violation.

Roger
 
I'm trying to follow the 5 amps versus 2 amps when a "screw is loosened".

I think the installation falls under "seperately derived systems" - but I'm not following some of the details as to what AE is experiencing. It certainly sounds like the Neutral and Equipment Grouding Conductor are bonded at some point where they shouldn't be - as he's seeing current flow in the EGC.

AE - can you clarify the details of the 5 amps versus 2 amps.


Brett
 
Brett, that is most likely due to the change in impedance of the metallic raceway path, tighten a locknut or screw and you lower the impedance of this path and more current will flow on it.

Roger
 
Gmack said:
When "starting over" with a XFMR we are now talking "service".

First panel/MDP etc cannot be isolated. Main bonding.

Maybe I read you wrong.
Click to expand...

The first panel of a separately derived system is not required to be bonded if the bonding is done at the source.

Take a look at 250.30(A)(1)
 
Roger

Roger

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Just my 2cents, Responding to Don and Iwire.

If we have current on a jumper to a bonding bushing from 5A to 2A when a srcew is loosed,then my guess is that the hard current favors a tight connection to the raceway and thus we have a parallel neutral "pretender"
 
Gmack said:
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If we have current on a jumper to a bonding bushing from 5A to 2A when a srcew is loosed,then my guess is that the hard current favors a tight connection to the raceway and thus we have a parallel neutral "pretender"
Click to expand...

I agree and like your term for it.

Roger
 
Gmack said:
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Just my 2cents, Responding to Don and Iwire.

If we have current on a jumper to a bonding bushing from 5A to 2A when a srcew is loosed,then my guess is that the hard current favors a tight connection to the raceway and thus we have a parallel neutral "pretender"
Click to expand...

I agree as well.
 
gamac,
Somebody figured it out back in the 99 cycle and the code was changed and inpectors in my area will not allow a EGC running side by side with a GC from a service or XFMR to a MDP/MD/CBP etc.

We used to run a EGC and GC together in such cases, but whats the point, for they are the same conductor and thus they "split" load and thats why the OP has his concerns about is meter registering current on a EGC.

P.S. we bond the XFMR case to the GC with a jumper inside the XFMR.
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You can't do it that way. The system bonding connection is either at the tansformer or the first disconnect. No matter where it is at, a bonding jumper is required between the transformer and the first disconnect.
Just my 2cents, Responding to Don and Iwire.

If we have current on a jumper to a bonding bushing from 5A to 2A when a srcew is loosed,then my guess is that the hard current favors a tight connection to the raceway and thus we have a parallel neutral "pretender"
Click to expand...
If there is current on a bonding connection for a SDS, then there is a parallel path and a code violation. My comments are directed at your statements that say you can't have a bonding conductor run along with the grounded conductor between the transformer and the first disconnect. This bonding conductor is required, not prohibited. The prohibition is on making more that one connection from the grounded conductor.
Don
 
Don

Don

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In a "grounded" service, the GC acts and serves the same as a EGC and all/everything is bonded to it on the line side.

It is not necessary to run a redundant EGC along side it and it is not required.

It creates a parallel path unless as you and Iwire say you "split" the connections at the Main. That provides no significant advantage and should someone connect a neutral on the grounding bus because we all know that the first panel is bonded as per 230, then we are back to the OP.

2cents.
 
Hey, I've had a full plate these past days, but i'm somewhat misquoted.. 5 amps to 2 amps when the screw is tightned was my post. I figure that the current drops across the screw because when tightned it essentially creates a parallel path as in ohms law for current in parallel circuits. It boggles my mind somewhat though because this means the ground has 2 potentials. How can I have a EGC bonded to the panel frame and they have different potentials. I have urged the removal of this neutral to ground bond as it may potentially be dangerous to personnel and sensitive equipment but I was overuled in fear that I may create a hazard otherwise. I have limited time to troubleshoot where this fault is. There are dozens of westinghouse pbd's and disconnects potentially wired as such. I update with my facility regarding code changes and either these panels were to code back then or the elec Cntr wired the same mistake over and over and over.
 
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Again - not quite following what screw you're tightening - but something is not quite making sense. Back to to Roger's post - if you lowered the impeadance - E=I * R - would say that R goes down, I would actually go up, not down. This would also be true if there was a parrallel path. Resistance goes down in one of the parrallel paths, then Rt would go down - again, I goes up.

Anyone shoot holes in this?

Brett
 
gmack,
In a "grounded" service, the GC acts and serves the same as a EGC and all/everything is bonded to it on the line side.
It is not necessary to run a redundant EGC along side it and it is not required.
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My understanding of this thread is that we are talking about SDS and not a service.
Don
 
Don

Don

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We treat a SDS as a service and everything that applys to a service we must apply to a SDS.

If I have a 100 SDS's in the same occupancy they must all follow the NEC rules as per a service and be treated separatley as services.

P.S. There used to be an exception for control wiring based on a SDS but I havent looked into that for awhile.
 
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Why run a grounded conduct and egc to the first disconnecting means when all you need is the grounded conduct? guschash
 
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